This power measuring game could throw up some surprises !!!!! especially
with so
many JEEPS about !!
Bang goes my New Year's resolution.
I did say that I would never get involved in this awful KEV stuff that is
polluting our reflector, but feel that I must say something. Otherwise you
get the situation (as history shows) where if a lie is told often enough it
becomes the 'truth'. Real truth is worth defending.
As regards transmitted power, as we are all aware (except for one) ERP is a
function of transmitted power and antenna size - the larger the antenna the
less power is required to reach the 1w ERP level. For a suburban sized
antenna you need a transmitter power greater than 1kW and several high power
transmitters were built. Two of these, one by G3KAU and the other by G3YXM
are shown in "The Low Frequency Experimenter's Handbook" pages 12 and 40. An
interesting design was shown in the "LF Experimenter's Source Book"
(forerunner of LFEH) by G3LNP which ran 4kV to the anode of a QYS-3000 to
produce 3kW O/P. He had calculated he needed that sort of power to get 1w
ERP from a simple vertical antenna.
By making the Decca transmitters available, G3JKV made a valuable
contribution to the LF community by showing us commercial design techniques,
such as the PA bridge configuration, tank circuit design and guard circuit
that were subsequently incorporated into the G4JNT high power transmitter.
I use a Decca transmitter but find it difficult to hit 1w ERP level. The
antenna is shown on page 57 of LFEH and has a calculated gain of -24dB1.
With 6.5amps I get a calculated 1.49w into the radiation resistance of the
antenna. However environmental effects such as trees reduce this by about a
half, which gives an ERP of around 800mW. This sort of power is only
achieved when the weather is relatively dry.
G3KEV's antenna has been described many times but the power and the antenna
current have not. The antenna is described as:
"The antenna I have been using for the recent Transatlantic QSO'S consists
of 4 inverted L's supported by a lattice tower at 105 ft high. Each L is 105
ft vertical and each one has a horizontal top section of
300 ft. The 4 vertical bottom ends converge to a common feed point 4 ft
above ground, connected to about 400 micro henry loading coil and has a
small series coil to ground used for resonating and fine tuning to get a 1:1
SWR.
Ground Radials consist of several 300 ft insulated wires, some connected at
the far end to sheep fencing. All the wire for antennas and radials is 2.5
mm insulated. The 4 inv L's are spaced at 90 degrees from each other around
the tower."
This antenna has a calculated gain (assuming good ground) of -16.6dBi. I am
not sure what transmitter is being used but a couple of years ago it was
400w. If this were connected to the antenna it would result in antenna
current of 3.5A and a calculated 3.8w into the radiation resistance of the
antenna. However if there are tall trees around the site this could reduce
it to around 2w ERP.
G3KEV has recently discovered transatlantic QSOs using QRSS:
"Solid fast QRS qso with VE1ZJ at 2 sec dot, almost there on normal CW. The
xband QSO only took a few minutes 136/7025 kHz solid copy both ways. I
understand previous QSO's took hours and days to complete."
The only QSO that I am aware of that took place over days was the 136kHz 2
way between G3AQC and VA3LK.
My QSOs, according to the log are as follows:
29/9/00 VE1ZJ on 14.043kHz, G3LDO on QRSS3, QSO time around 20mins
13/2/01 VE1ZZ on QRSS3, G3LDO on QRSS10, 136kHz 2 way. (VE3ZJ receiver link
via 80m) QSO time 50mins
21/2/01 VE1ZZ on QRSS3 136kHz G3LDO on 3512kHz QSO time 15mins.
I am not getting involved in this stuff any more - I will go and join the
silent majority.
Regards,
Peter, G3LDO
e-mail <[email protected]>
Web <http://web.ukonline.co.uk/g3ldo>
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